This paper compares the mechanical properties of different natural fiber composites produced by rotational molding as a way of waste valorization from campaigns to control invasive plant species in Macaronesia. Rotomolded parts produced with polymeric matrices (polyethylene) and filled with up to 20% by weight of cellulosic fibers obtained from Arundo donax L., Pennisetum setaceum, and Ricinus communis plants were characterized in terms of tensile, flexural, and impact strength. It was found that the sieving of natural fibers allowed for their introduction in higher loadings, from 10 (for un-sieved material) to 20%; fiber size greatly affected the mechanical properties of the final parts, although some combinations were proven not to reduce the mechanical properties of the neat resin. This study is a first approach to the valorization of residues obtained from periodic campaigns of the control of invasive species performed by public authorities, usually at the local level. It is important to highlight that the main objective of this research did not focus on economically profitable activity; instead, it was focused on the reduction of wastes to be disposed from ecosystem maintenance actions and the investment of potential income into preservation policies.

This paper summarises the results obtained from the characterisation of giant reed (Arundo donax L.) plant and fibres. The research is part of a project developed in the Macaronesia region, of which the aim is to demonstrate the feasibility of using biomass from invasive plant species in the composites sector as a way of financing control campaigns and habitats conservation labours. An experimental procedure for the extraction of fibre bundles from this plant was developed, and the material obtained was characterised in terms of chemical composition, thermogravimetry and infrared spectra to evaluate its potential application in the production of polymeric composite materials as a strategy for the valorisation of residual biomass from this invasive species in Macaronesia. Thermoplastic matrix composites with fibre content up to 40 wt.% were produced and their mechanical properties under tensile, flexural and impact loading were determined. No references on the preparation of composite materials with polyolefin matrices and giant reed fibres have been found. Results obtained from mechanical tests show a good performance of the manufactured composites, with a significant increase in both flexural and tensile stiffness; the flexural modulus is almost tripled for PE-based composites and rises to 88% with respect to PP matrix. The ultimate flexural strength and the tensile and flexural yield strength are kept at acceptable values compared to neat polymer materials, although ultimate tensile strength and impact resistance are significantly affected when natural fibres are added.

Some studies have evaluated the use of Opuntia as reinforcement for polymeric matrices, obtaining good results in energy absorption tests and increasing the tensile elastic modulus. However, no studies focusing on the previous characterisation of the fibres and their treatment to improve compatibility with polymeric matrices have been found. This work analyses the chemical composition of Opuntia maxima (OM) and Opuntia dillenii (OD) cladodes and fibre, studying how different treatments influence it. AOAC 2000 methods were used to determine non-structural components and the Van Soest method was used to estimate structural components. Surface characteristics of the samples were also evaluated by Fourier Transform Infrared Spectroscopy (FTIR). Opuntia fibre presented higher cellulose (50–66%) and lignin (6–14%) content and lower hemicellulose (8–13%) content than Opuntia cladodes (9–14% cellulose, 20–50% hemicellulose, 1–4% lignin). Despite the variability of lignocellulosic materials, OD cladodes treated with water and acetic acid achieved an increase in the structural components. Alkaline fibre treatment removed pectin and hemicellulose from the fibre surface, slightly increasing the cellulose content. Future research should evaluate whether the treated Opuntia fibre can improve the mechanical properties of reinforced polymer.

This paper assesses the modifications in the properties of rotomolded polyethylene (PE) and polylactic acid (PLA) composites obtained with 5 and 10% giant reed fibers, mainly focusing on the alterations due to a bio-disintegration process. Thermal properties (melting temperature and crystallinity degree), morphology (via optical and scanning electron microscopy), and chemical changes (by Fourier Transformed Infrared spectroscopy) were studied. Composites with untreated and NaOH-treated fibers were obtained, finding that this treatment does not improve the mechanical performance of composites due to increased porosity. The introduction of natural fibers into a PE matrix does not significantly modify the thermal and bio-disintegration properties of the rotomolded material. Regarding mechanical properties, PE-composites show increased tensile modulus and reduced impact and tensile strength than the matrix. On the other hand, PLA composites show lower impact and flexural strength than neat PLA, remaining the rest of the mechanical properties unchanged regardless of the fibers' addition. The incorporation of Arundo fibers modifies to a great extent the thermal and degradation behavior of the PLA matrix.

Rotational molding allows for obtaining hollow parts with good aesthetics and properties, having as main drawbacks the lack of pressure and the long cycle times, which limit the range of materials. Different fillers have been introduced in rotomolding to obtain composite materials assessed. This review has shown that glass fibers or particles are the most common material among them, although carbon fibers or clays have also been studied. In general terms, 10% loadings provide an increase in mechanical properties; higher loadings usually lead to a decrease in processability or final properties. When the filler consists of a micro- or nano-material, such as clay or graphene, lower loadings are proposed, generally not exceeding 3%. The use of fillers of an inorganic nature to obtain composites has not been as explored as the incorporation of lignocellulosic materials and even less if referring to waste materials or side streams from industrial processes. So, there is a broad field for assessing the processing and properties of rotomolded composites containing inorganic waste materials, including the study of the relationship between the ratio of filler/reinforcement and the final properties and also their preprocessing (dry blending vs. melting compounding).

The wide range of applications and the numerous advantages of plastics have led to their excessive use, with subsequent damage to ecosystems. As an environmentally friendly alternative, biocomposites have gained much attention, and microalgae have become a potential source for their production. In this study, the use of washed and unwashed Spirulina in polyethylene-based composites has been evaluated as a way to prevent the thermooxidation of polyethylene, while at the same time, reducing the amount of virgin plastic used. Biocomposites were produced by rotomolding, testing different biomass contents and determining their mechanical and thermal performances as well as their water uptake level. Composites with up to 15% of biomass (by weight), a particularly high ratio for rotomolding, were satisfactorily produced. Using 5% of both biomasses did not significantly modify the behavior when compared with the neat PE samples’ properties. For higher loadings, the use of non-washed biomass allowed us to obtain better properties, with added benefits related to using an unwashed biomass (less water consumption, lower costs and fewer environmental impacts). On the other hand, this study showed a promising beneficial effect on the thermooxidative resistance of composites, as the oxidation induction times were notably increased with biomass addition.